Early transition metal catalysts for producing olefin polymers by coordination polymerization are well-known. Typically these are the traditional Ziegler-type catalysts based on metals from Groups 4 and 5 of the Periodic Table (IUPAC new notation) and the newer metallocene or similar catalysts based on Groups 4 to 8 metals. There is, however, also interest in catalysts based on late transition metals, such as nickel, since these frequently exhibit greater tolerance to polar functional groups than Group 4 to 8 initiators. Polar-tolerant olefin polymerization catalysts may allow the use of cheaper, less pure monomer feeds, and may also offer new product possibilities through the potential incorporation of polar comonomers.
Polymers containing polar functionalities, particularly oxygen- and nitrogen-containing groups, are useful in applications such as flexible packaging, durables, adhesives, and gas- or oil-resistant barrier films. In addition, catalysts which display a high tolerance to polar groups are useful for normal olefin polymerization in the presence of polar poisons such as dimethyl ether.
Considerable research has been directed to the production of ligand frameworks that provide many sites for steric and electronic modification since these offer the possibility of generating a large number of catalysts tailored for specific functions. By way of example, bidentate ligands featuring N,N-, N,O-, P,O-, or N,P-chelation are widely used in the synthesis of transition metal catalysts for olefin oligomerization, trimerization, polymerization, and copolymerization.
Bidentate N,P-binding structures have been incorporated into both highly active Group 4 and 6 based catalysts (Ti, Zr, and Cr) and polar-tolerant late transition metal catalysts (Ni and Pd). For example, Ti, V, Cr, Co, Ni, and Pd complexes containing neutral phosphine-imine or phopshine-amine ligands with four, five, and six membered ring chelation have been used as ethylene oligomerization and polymerization catalysts (see International Patent Publication Nos. WO 03/078478, WO 00/59956, WO 01/92342, and WO 98/40420; Japanese Published Patent Application No. JP2000/128922; Daugulis et al. Organometallics 2002, 21, 5926-5934; Guan et al. Organometallics 2002; 21, 3580-3586; van den Beuken et al. J. Chem. Soc., Chem. Commun. 1998, 223-224; and Keim et al. J. Organomet. Chem. 2002, 662, 150-171). However, in many cases, the polyethylenes obtained with such catalysts are highly branched and of low molecular weight. Neutral Pd phosphine-imines have also been used for olefin/carbon monoxide (CO) copolymerization (see, for example, Chen et al. Organometallics 2001, 20, 1285-1286; and Reddy et al. Organometallics 2001, 20, 1292-1299).
In addition to these species incorporating neutral bidentate ligands, Ni complexes incorporating monoanionic phosphine-amide ligands with four- and five-membered ring chelation have been shown to be active for ethylene polymerization and ethylene/norbornene copolymerization (see International Patent Publication Nos. WO 03/31485 and WO 01/92342).
Mixed nitrogen-phosphorus ligands having a total of three N or P atoms, yet exhibiting a bidentate binding mode, have also been used in both early and late transition metal catalysts. For example, neutral P,N,P ligands have been incorporated into complexes of Cr (for ethylene trimerization), Ni (for olefin polymerization), and Pd (for olefin/CO copolymerization) (see, for example, International Patent Publication Nos. WO 01/10876, WO 00/06299, and WO 97/37765; Cooley et al. Organometallics 2001, 20, 4769-4771; Carter et al. J. Chem. Soc., Chem. Commun. 2002, 858-859; and Dossett et al. J. Chem. Soc., Chem. Commun. 2001, 699-700). These complexes have four-membered ring ligand chelation with the two P atoms binding to the metal center. The two P atoms are linked via direct P—N bonds to a single non-binding nitrogen atom.
Similarly, monoanionic iminophosphonamide N,P,N ligands having direct N—P—N linkages and undergoing four-membered ring N,N-ligand coordination have been used to prepare Ti, Zr, and Ni complexes active for olefin polymerization. See, for example, Vollermaus et al. Organometallics 1999, 18, 2731-2733 and Schubbe et al. Macromol. Chem. Phys. 1995, 196, 467-478.
Phosphine-imidazoles and pyrimidyl-phosphines are N,N,P ligands containing two nitrogen atoms and one phosphorus atom, all of which are attached to a central carbon atom, wherein the two N atoms form part of an unsaturated five- or six-membered heterocylic ring. Pyrimidyl-phosphines are neutral, whereas phosphine-imidazoles may be may be neutral or monoanionic depending on the pattern of N-substitution. Due to the heterocyclic ring structure, neither phosphine-imidazoles or pyrimidyl-phosphines can be subjected to independent variation of the substituents present at each N atom, nor can they undergo bidentate N,N-binding. These ligands tend to bind to a metal in a monodentate fashion through only one donor atom, or to two metals simultaneously in a bridging (dimeric) fashion, which may negatively affect catalytic activity. For example, dimeric Pd complexes with bridging phosphine-imidazole ligands have been found to be inactive for ethylene/CO polymerization by Done et al. (J. Organomet. Chem. 2000, 607, 78-92). However, in contrast, a monomeric pyrimidyl-phosphine Pd complex with bidentate, four-membered ring P,N coordination was found to be active for alkyne carbonylation by Reetz et al. (Tetrahedron Lett. 1998, 39, 7089-7092).
International Patent Publication No. WO 01/92342 describes monoanionic, bidentate N,N,P ligands and Ni complexes of such ligands that are active for olefin polymerization. In these complexes, the Ni atom is bound to the P atom and to one negatively charged N atom in a five-membered ring arrangement. However, although the two N atoms are bound to a single central carbon, the P atom is not bound to the same central carbon atom.
Phosphaguanidinate ligands are monoanionic N,N,P ligands in which the phosphorus atom and two nitrogen atoms are all attached to a central carbon atom and are not part of a heterocyclic structure. A phosphaguanidinate ligand can undergo binding to a transition metal through one N atom and the P atom or, alternately through both N atoms, in a bidentate, four-membered-ring fashion.
Phosphaguanidinate ligands of the structure [Ph2PC(N-p-tolyl)(NH-p-tolyl)] and complexes of the structure [Ph2PC(N-p-tolyl)(N-p-tolyl)]Mt(PPh3)2 (where Mt is Rh or Ir), which have four-membered-ring P,N-coordination, have been prepared by Thewissen et al. (J. Organomet. Chem. 1980, 192, 101-113 and 115-127 and Rec. Trav. Chim. Pays-Bas 1980, 99, 244-246). These ligands and complexes have not been used for polymerization reactions, lack ortho-substitution on their N-aryl (tolyl) substituents, and are unstable under certain conditions and to certain reactants. N-aryl ortho-substituents are known to play an important role in manipulating the behavior of mid- and late-transition metal olefin polymerization/oligomerization catalysts (see, for example, Johnson et al. J. Am. Chem. Soc. 1995, 117, 6414-6415 and Britovsek et al. Chem. Eur. J. 2000, 6, 2221-2231).
Phosphaguanidinate complexes of Zr containing four-membered ring N,N binding have been prepared via insertion of an RN═C═NR fragment (where R is phenyl or isopropyl) into the Zr—P bond of (Cp)2ZrCl{P(SiMe3)2} (where Cp=C5H5 or C5H4Me). See Hey-Hawkins et al. Z. Naturforsch, B 1993, 48, 951-957 and Lindenberg et al. Polyhedron 1996, 15, 1459-1471. These phosphaguanidinate ligands have silyl rather than carbon substituents at the P atom and the ligand salt Li[P(SiMe3)2C(NPh)(NPh)] could not be successfully prepared by reaction of Li[P(SiMe3)2] with PhN═C═NPh in the absence of Zr. These ligands and complexes have also not been used for polymerization reactions.